Around 500 dignitaries and world leaders are expected to come to London to pay their respects, including US President Joe Biden.
They will join members of the royal family and Liz Truss, as well as past prime ministers, for the historic service at Westminster Abbey at 11am on Monday.
Speaking to the PA news agency, one Whitehall source said: “This is the biggest international event we have hosted in decades.”
The source said the logistics of the event, including transport and security, was like organising hundreds of state visits within days.
Invitations were sent over the weekend to heads of state of countries where the UK has diplomatic relations. For most countries, the head of state is allowed to bring a guest.
However, Vladimir Putin, his ally Aleksandr Lukashenko of Belarus, and leaders in Myanmar have not been invited, the source said.
The leaders of most Commonwealth countries are expected to attend, with New Zealand's prime minister Jacinda Ardern saying she would make a nearly 24-hour journey to attend.
Her Canadian and Australian counterparts, Justin Trudeau and Anthony Albanese, have also confirmed they will attend.
Mr Albanese said he would not be travelling alone and that the Palace had invited him to bring along “10 Australians who have made extraordinary contributions to their communities".
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France's Emmanuel Macron, Germany's Frank-Walter Steinmeier, Italy's Sergio Mattarella, Turkey's Recep Tayyip Erdogan and Brazil's Jair Bolsonaro are among the presidents attending, along with the European Commission's Ursula von der Leyen.
King Felipe of Spain and his wife, Queen Letizia, are among the European royals who will attend.
However, it is not thought the trip will be made by Ukraine's president Volodymyr Zelensky, who took time out from organising his country's fightback against Russian forces to sign a book of condolence for the Queen.
Downing Street on Monday refused to comment on reports that world leaders visiting London for the Queen's state funeral have been asked to travel on commercial flights and will be bussed to Westminster Abbey.
